– Delaney Knorr
Evolutionary theory has long supported the idea that, among humans, allomothers are critical players in improving offspring fitness. Allomothers are kin, or less commonly non-kin, who help out the mother-offspring dyad. Often allomothers help by providing food, child care, or various forms of social support that increase offspring fitness. But from an evolutionary perspective, when do allomothers start helping the mother-child dyad? Much of the anthropological research has focused on weaning as a critical point of intervention for allomothers because this is a vulnerable life stage for the offspring. However, there are many vulnerable periods of development. Recently, looking to earlier life stages, scholars have shown that allomothers play a critical role in breastfeeding by teaching mothers how to properly breastfeed and emotionally supporting them to continue to do so. Additionally, even earlier, having allomothers around to emotionally support the mother during childbirth and physically aid in catching the baby are critical for offspring fitness. What about even before the birth– do allomothers assist during pregnancy? We offer one of the first perspectives to consider a prenatal allomaternal effect.
Pregnancy is a critical time of development where the mother and fetus are vulnerable to stress. Indeed, the developmental origins of health and disease framework has established connections between stressors and stress experienced during pregnancy, adverse birth outcomes, and long-term health disparities. Thus, evolutionary biologists may expect allomothers to start investing in the mother-child well-being during utero for these benefits to offspring fitness.
In this paper, we take an evolutionary perspective to ask how allomothers may help during pregnancy. We focus on (soon-to-be) grandmothers in this paper as they have (1) clear inclusive fitness benefits, (2) related reproductive experiences to the (soon-to-be) mother, and (3) greater reproductive expertise than other kin categories. We also focus on three relationship characteristics: geographic proximity, emotional social support, and communication levels. Geographic proximity has often been shown to be an important relationship characteristic in previous studies on allomothers. These studies are usually conducted with societies that had no way to provide other kinds of support without being geographically close-by. Thus, geographic proximity is a good proxy for the help that is done in person, like chores or food provisioning. However, our study investigates other kinds of support that do not need to be transmissible in person today, such as communication and emotional social support.
Our study makes use of survey data from 216 pregnant women living in Southern California. These women all identified as Latina (a diverse ethnic category referring to Latin American heritage), were of various socio-economic backgrounds (e.g., food security and education levels), and represented the full range of trimesters. Latinas living in the U.S. tend to live in three-generation homes more commonly than other groups. Additionally, the cross-cultural importance of family among this group is a helpful context in which to ask about experiences of family. We discuss possible cultural explanations in the full paper.
We asked how each grandmother influenced three independent measures of maternal mental health: depression, anxiety, and pregnancy-related anxiety. Each model tested a different relationship characteristic among both the maternal grandmother and paternal grandmother, while controlling for the effects of father relationship characteristics.
Our findings show that greater levels of emotional support from and communication with maternal grandmothers were significantly associated with lower levels of depression, above the effects of fathers in the same categories. While our study only looks at maternal mental health, other studies have found that depression was tied to low-birth weight and preterm birth, which in turn have been associated with various morbidities and mortality.
We would expect from a developmental origins of health and disease perspective that both grandmothers may be interested in offsetting maternal stress, for the sake of the offspring. Instead, we find (consistent with other allomother literature) that maternal grandmothers are statistically more influential allomothers than paternal grandmothers. This may be due to the long-term mother/daughter relationships that are distinct from mother-in-law/daughter-in-law ones, or perhaps due to other evolutionary explanations discussed in the full paper.
Our results also add to the growing evidence that geographic proximity itself is not always a critical component of grandmaternal allomothering. This finding also suggests some feasible implications for public health. Funding call minutes, phones, and internet connections to increase a family’s ability to stay in contact with each other, when living across borders or when visitation is otherwise not possible, could positively contribute to perinatal mental health.
We suggest that grandmaternal allomothering includes the prenatal period. We observe that social support and communication with maternal but not paternal grandmothers are associated with mental health benefits for mothers. More work is needed to connect this prenatal grandmaternal influence to offspring postnatal outcomes. By including measures of grandmaternal instrumental support and infant outcomes, future work could also further our understanding of grandmaternal involvement in the context of fetal programming.
Read the original paper here.
Knorr and Fox (2023). An evolutionary perspective on the association between grandmother-mother relationships and maternal mental health among a cohort of pregnant Latina women. Evolution and Human Behavior, 44(1): 30–38.